Resin particles are conventionally known that are produced by dispersing, in an aqueous medium, a resin solution in which the resin was dissolved in a solvent in advance in the presence of a dispersing (assistant) agent such as a surfactant or water-soluble polymer, and then removing the solvent via heating, pressure reduction, or the like (the solution resin suspension process). The shapes of these resin particles obtained by the solution resin suspension process are difficult to be regulated, and in general they have a spherical form.
Use of the spherical particles as a paint additive or a cosmetics additive leads to insufficient masking properties in some cases. When the particles are used as a paper coating additive, the retention of ink is sometimes poor due to lack of oil absorbance. When the particles are used as an abrasive, the frictional resistance is small, thereby grinding properties are poor in some cases. The use of the particles as a toner resin poses the problem of rendering cleaning properties insufficient when the toner remaining on a photoreceptor without being transferred to a paper surface is cleaned with a blade. For solution of such problems, a process is available that involves appropriately elasticizing the surfaces of particles prior to volume shrinkage of the particles with a solvent-removing, and making smaller the surface area decreasing speed than the volume shrinking speed to form resin particles having unevenness on the surfaces. As a means of rendering the surface of a particle to be elastic is proposed a method of forming a shell material on the resin particle surface by means of interfacial polymerization or in-situ polymerization (refer to Japanese Patent Application Laid-Open No. 4-209630). This method, however, does not sufficiently exhibit properties required for the particles due to the effect of the shell material. For instance, a toner in this case causes the problem of lowering low-temperature fixing properties and anti-hot offset properties, thereby extremely narrowing the fixing temperature range.